Receiving apparatus that receives packet signal

ABSTRACT

An RF unit receives predetermined signals. The RF unit amplifies the received signals. A gain control unit controls the gain at the RF unit based on the amplified signal and has the RF unit use the controlled gain. The gain control unit performs different controls on the received signals, depending on the case when the received signal is a known signal placed in the beginning of packet signal and the case when the received signal is a signal other than the packet signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of U.S. Ser. No. 13/768,791filed Feb. 15, 2013, now U.S. Pat. No. 9,112,577, which is aContinuation Application of PCT/JP2011/007134, filed on Dec. 20, 2011,which claims priority of Japanese Patent Application No. 2011-015715,filed on Jan. 27, 2011, Japanese Patent Application No. 2011-041987,filed on Feb. 28, 2011, Japanese Patent Application No. 2011-041989,filed on Feb. 28, 2011, Japanese Patent Application No. 2011-041988,filed on Feb. 28, 2011, Japanese Patent Application No. 2011-041990,filed on Feb. 28, 2011. The subject matter of each is incorporatedherein by reference in entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a receiving technology, and itparticularly relates to a receiving apparatus that receives packetsignal.

2. Description of the Related Art

Road-to-vehicle communication has been under investigation in an effortto prevent collision accidents of vehicles on a sudden encounter at anintersection. In a road-to-vehicle communication, information onconditions at an intersection is communicated between a roadside unitand an in-vehicle unit. Such a road-to-vehicle communication requiresinstallation of roadside units, which means a great cost of time andmoney. In contrast to this, an inter-vehicular communication, in whichinformation is communicated between in-vehicle units, has no need forinstallation of roadside units. In that case, current positioninformation is detected in real time by GPS (Global Positioning System)or the like and the position information is exchanged between thein-vehicle units. Thus it is determined on which of the roads leading tothe intersection the driver's vehicle and the other vehicles arelocated.

When packet signals are received in wireless LAN compatible with theIEEE 802.11 standard and the like, the gain or amplification factor ofan amplifier for amplifying the packet signals is set based on STF(Short Training Field) placed in the beginning of packet signal. Theamplification suited to the received packet signal is not done if theaccuracy in the setting of gain is low.

SUMMARY OF THE INVENTION

The present invention has been made in view of the foregoingcircumstances, and a purpose thereof is to provide a technology forsetting the gain suitable to a received packet signal.

In order to solve the above-described problems, a receiving apparatusaccording to one embodiment of the present invention includes: areceiving unit configured to receive a signal; an amplifier configuredto amplify the signal received by the receiving unit; and a control unitconfigured to control a gain in the amplifier based on a signalamplified by the amplifier and configured to have the amplifier use thecontrolled gain. The control unit performs different controls on thesignals received by the receiving unit, depending on a case when thereceived signal is a known signal placed in the beginning of packetsignal or a case when the received signal is a signal other than thepacket signal.

Optional combinations of the aforementioned constituting elements, andimplementations of the invention in the form of methods, apparatuses,systems, recording media, computer programs and so forth may also bepracticed as additional modes of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described by way of examples only, withreference to the accompanying drawings which are meant to be exemplary,not limiting and wherein like elements are numbered alike in severalFigures in which:

FIG. 1 shows a structure of a communication system according to anexemplary embodiment of the present invention;

FIG. 2 shows a structure of a radio apparatus mounted on a vehicle shownin FIG. 1;

FIG. 3 shows a format of packet signal defined in the communicationsystem of FIG. 1;

FIG. 4 shows a structure of a receiving apparatus in the radio apparatusof FIG. 1;

FIG. 5 is a data structure of a table stored in a decision unit of FIG.1;

FIGS. 6A and 6B show an operational overview of a decision unit of FIG.3;

FIG. 7 shows a structure of an instruction unit shown in FIG. 4;

FIG. 8 shows an operational overview of the instruction unit shown inFIG. 7;

FIG. 9 is a data structure of a table stored in an instruction unit ofFIG. 4;

FIG. 10 is a flowchart showing a procedure, for setting an averageperiod and a target value, performed by the receiving apparatus of FIG.4;

FIG. 11 is a flowchart showing a procedure, for controlling the gain,performed by the receiving apparatus of FIG. 4;

FIG. 12 is a flowchart showing a procedure, for setting ranges,performed by the receiving apparatus of FIG. 4;

FIG. 13 is a flowchart showing a procedure, for storing the gain,performed by the receiving apparatus of FIG. 4;

FIG. 14 is a flowchart showing a procedure, for setting an initialvalue, performed by the receiving apparatus of FIG. 4;

FIG. 15 is a flowchart showing an instructing procedure performed by thereceiving apparatus of FIG. 4;

FIG. 16 shows an operational overview of an instruction unit accordingto a modification of an exemplary embodiment; and

FIG. 17 shows a structure of a receiving apparatus according to anothermodification of an exemplary embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described by reference to the preferredembodiments. This does not intend to limit the scope of the presentinvention, but to exemplify the invention.

Our knowledge underlying the present invention will be explained beforeexemplary embodiments of the present invention are explained in detail.An access control function called CSMA/CA (Carrier-Sense Multiple Accesswith Collision Avoidance) is used in wireless LAN (Local Area Network)compliant with IEEE 802.11 and the like. Thus, the same radio channel isshared by a plurality of terminal apparatuses. In such a scheme as CSMA,a packet signal is transmitted after it has been verified by carriersense that other packet signals are not transmitted. Here, when wirelessLAN is applied to the inter-vehicular communication such as ITS, a needarises to transmit information to a large indefinite number of terminalapparatuses, and therefore it is desirable that signals be sent bybroadcast.

When a packet signal is received in wireless LAN compliant with IEEE802.11 and the like, the gain of an amplifier for amplifying the packetsignal is set based on STF (Short Training Field) placed at a beginningpart of packet signal. If gain setting accuracy is low, amplificationsuited to the received packet signal will not be done. If, for example,the gain is low for a packet signal whose received power is low or thegain is high for a packet signal whose received power is high, thedemodulation accuracy in demodulating the packet signal willdeteriorate. Thus a gain best suited to the received packet signal isdesirably set.

Exemplary embodiments of the present invention relate to a communicationsystem that carries out not only an inter-vehicular communicationbetween terminal apparatuses mounted on vehicles but also aroad-to-vehicle communication from a base station apparatus installed inan intersection and the like to the terminal apparatuses. As theinter-vehicular communication, a terminal apparatus transmits, bybroadcast, a packet signal in which the information such as thetraveling speed and position of the vehicle is stored. And the otherterminal apparatuses receive the packet signals and recognize theapproach or the like of the vehicle based on these items of information.Further, the base station apparatus sends, by broadcast, a packet signalin which information concerning traffic jam and road repairinginformation are stored. The terminal apparatus recognizes the occurrenceof traffic jam and a section and route where the road is underconstruction.

The format used in the communication system is similar to that used inwireless LAN and is such that STF is placed at a beginning part and LTF(Long Training Field) is placed following STF. LTF contains two OFDMsymbols; the first (front) one is called “LTF1” and the second (rear)one is called “LTF2”. As a packet signal is received in wireless LAN,the gain of the amplifier is generally controlled through automatic gaincontrol (AGC) before the packet signal is demodulated and so forth. Inorder to reduce the processing amount and power consumption for AGC, theAGC processing is stopped while no packets is being received. Then, amaximum value is set as the gain in order that packet signals can bedetected even though the AGC processing is stopped. If a packet signalwhose received power is large is received in such a situation, thepacket signal will tend to be distorted. If a packet signal with a smallreceived power is being received, such a packet signal may not beamplified to a level required for demodulation if the gain is small. Asa result, the receiving characteristics get degraded. It is thereforerequired that a gain best suited to the received packet be set.

To cope with this, a receiving function implemented in a base stationapparatus and terminal apparatuses in the communication system accordingto the present exemplary embodiments (hereinafter referred to as“receiving apparatus”) performs the following processing. That is, areceiving apparatus controls the gain even in a period during which nopacket signals is received. More stable operation than the quicktracking of propagation environment is desired in such a period duringwhich no packet signals is received. Thus, in such a period, a periodover which the received signals are averaged (hereinafter this periodwill be referred to as “average period”) is made longer, a target valueof received signal after amplification is set to a smaller value, andthe frequency of updating the gain is set lower by the receivingapparatus. Immediately after completion of the receiving of packetsignals, the receiving apparatus uses the gain that was used before thereceiving of the packet signal. If, on the other hand, the amplifiedpacket signal is included in a target range during the receiving ofpacket signal, controlling the gain will be stopped and the gain will befixed. If the gain becomes maximum during a control operation, thereceiving apparatus will enlarge the target range for the purpose ofpreventing the gain from dropping and terminating the control operationas early as possible.

FIG. 1 shows a structure of a communication system 100 according to anexemplary embodiment of the present invention. FIG. 1 corresponds to acase thereof at an intersection viewed from above. The communicationsystem 100 includes a base station apparatus 10, a first vehicle 12 a, asecond vehicle 12 b, a third vehicle 12 c, a fourth vehicle 12 d, afifth vehicle 12 e, a sixth vehicle 12 f, a seventh vehicle 12 g, and aneighth vehicle 12 h, which are generically referred to as “vehicle 12”or “vehicles 12”, and a network 80. It is to be noted that each vehicle12 has a not-shown terminal apparatus mounted therein. Also, an area 82is formed around the base station apparatus 10, and analmost-unreachable area 84 is formed outside the area 82.

As shown in FIG. 1, a road extending in the horizontal, or left-right,direction and a road extending in the vertical, or up-down, direction inFIG. 1 intersect with each other in the central portion thereof. Notehere that the upper side of FIG. 1 corresponds to the north, the leftside thereof the west, the down side thereof the south, and the rightside thereof the east. And the portion where the two roads intersecteach other is the intersection. The first vehicle 12 a and the secondvehicle 12 b are advancing from left to right, while the third vehicle12 c and the fourth vehicle 12 d are advancing from right to left. Also,the fifth vehicle 12 e and the sixth vehicle 12 f are advancingdownward, while the seventh vehicle 12 g and the eighth vehicle 12 h areadvancing upward.

In the communication system 100, the base station apparatus 10 isinstalled at the intersection. The base station apparatus 10 receivesthe traffic jam information and the road repairing information from thenetwork 80. The base station apparatus 10 generates a packet signal inwhich the traffic jam information and the road repairing information arestored, and broadcasts the thus generated packet signal containing suchitems of information. Note that the thus generated packet containingsuch items of information is broadcast to the terminal apparatuses thatare present within the second range 212 formed around the base stationapparatus 10. As a terminal apparatus mounted on the vehicle 12 receivesa packet signal from the base station apparatus 10, the terminalapparatus extracts the traffic jam information and the road repairinginformation stored in the packet signal. The terminal apparatus conveysthe extracted traffic jam information and road repairing information toa driver. The extracted traffic jam information and road repairinginformation may be conveyed through a display of the information on amonitor, for instance. The terminal apparatus acquires informationregarding the present position through GPS or the like and generates apacket signal in which the information on the present position isstored. The terminal apparatus broadcasts the packet signal by CSMA/CA.As the terminal apparatus receives a packet signal from another terminalapparatus, the terminal apparatus notifies the driver that a vehicle 12where the other terminal apparatus is mounted is approaching.

FIG. 2 shows a structure of a radio apparatus 20 mounted on the vehicle12. The radio apparatus 20 includes an RF unit 22, a modem unit 24, aprocessing unit 26, and a control unit 28. The radio apparatus 20corresponds to a terminal apparatus mounted on the vehicle 12 of FIG. 1but it may correspond to the base station apparatus 10 of FIG. 1.Hereinafter, the terminal apparatuses and the base station apparatus 10will be generically referred to as “radio apparatus 20” or “radioapparatuses 20” (first case), and there may also be cases where theterminal apparatus or the base station apparatus 10 is called “radioapparatus 20” (second case). However, no distinction will be madebetween the first case and the second case.

As a receiving processing, the RF unit 22 receives, through the antenna,packet signals transmitted from other radio apparatuses 20 (not shown).The RF unit 22 performs a frequency conversion on the received packetsignal of a radiofrequency and thereby generates a packet signal ofbaseband. Further, the RF unit 22 outputs the baseband packet signal tothe modem unit 24. Generally, a baseband packet signal is formed of anin-phase component and a quadrature component, and therefore it shouldbe represented by two signal lines. However, it is represented by asingle signal line here to make the illustration clearer forunderstanding. The RF unit 22 also includes an LNA (Low NoiseAmplifier), a mixer, an AGC (Automatic Gain Control) unit, and an A/Dconverter.

As a transmission processing, the RF unit 22 performs a frequencyconversion on the baseband packet signal inputted from the modem unit 24and thereby generates a radiofrequency packet signal. Further, the RFunit 22 transmits, through the antenna, the radiofrequency packet signalin a road-to-vehicle transmission period. The RF unit 22 also includes aPA (Power Amplifier), a mixer, and a D-A converter.

As a receiving processing, the modem unit 24 demodulates theradiofrequency packet signal fed from the RF unit 22. Further, the modemunit 24 outputs the demodulation result to the processing unit 26. As atransmission processing, the modem unit 24 modulates the data fed fromthe processing unit 26. Further, the modem unit 24 outputs themodulation result to the RF unit 22 as a baseband packet signal. It isto be noted here that the communication system 100 is compatible withthe OFDM (Orthogonal Frequency Division Multiplexing) modulation schemeand therefore the modem unit 24 performs FFT (Fast Fourier Transform) asa receiving processing and performs IFFT (Inverse Fast FourierTransform) as a transmission processing also.

A description is now given of the format of packet signal that is to bemodulated and demodulated by the modem unit 24. FIG. 3 shows a format ofpacket signal defined in the communication system 100. As shown in FIG.3, STF is assigned to the beginning of packet signal. And the STF isfollowed by GI2, LTF1, LTF2, SIG, and Data. STF is a signal of 160samples where a signal of 16 samples is repeated ten times. That is, inSTF, a signal pattern whose period is shorter than that of LTF1described later is repeated ten times. LTF1 and LTF2 are periodic of 64samples in common with each other and are of the identical signalpattern. GI2 is a guard interval for LTF1 or LTF2 and is of 32 samples.GI2, LTF1, and LTF2 constitute LTF. Note here that LTF may beconstructed of LTF1 and LTF2. SIG is a control signal and is of 80samples. This 80-sample SIG contains a guard interval of 16 samples.Refer back to FIG. 2.

As a receiving processing, the processing unit 26 receives thedemodulation result by the modem unit 24. The processing unit 26performs a processing according to the demodulation result. If, forexample, the demodulation result is information concerning the presentposition of the vehicle 12 in which the other radio apparatus ismounted, the processing unit 26 will convey the approach or the like ofthe not-shown other vehicle 12 to the driver via a monitor or speaker.If the demodulation result is the traffic jam information and the roadrepairing information, the processing unit 26 will convey them to thedriver via the monitor or speaker. And the present position, travelingdirection, traveling speed and so forth of a not-shown vehicle 12,namely the vehicle 12 carrying the radio apparatus 20 are acquired basedon data supplied from the aforementioned not-shown components of theprocessing unit 26. Hereinafter the present position, travelingdirection, traveling speed and so forth will be generically referred toas “present position” or “positional information”. The present positionthereof is indicated by the latitude and longitude. Known art may beemployed to acquire them and therefore the description thereof isomitted here. The processing unit 26 generates a packet signal in whichthe present position is stored. The processing unit 26 outputs thepacket signal to the modem unit 24. The control unit 28 controls theoperation timing of the radio apparatus 20.

These structural components may be implemented hardwarewise by elementssuch as a CPU, memory and other LSIs of an arbitrary computer, andsoftwarewise by memory-loaded programs or the like. Depicted herein arefunctional blocks implemented by cooperation of hardware and software.Therefore, it will be obvious to those skilled in the art that thefunctional blocks may be implemented by a variety of manners includinghardware only or a combination of hardware and software.

FIG. 4 shows a structure of a receiving apparatus 30 in the radioapparatus 20. The receiving apparatus 30 includes an RF unit 22, a gaincontrol unit 32, an STF correlation computing unit 34, a rising-edgedetector 36, a state management unit 38, and a demodulation/receivingprocessing unit 40. The gain control unit 32 includes a powercalculating unit 42, a decision unit 44, and an instruction unit 46.

As described above, the RF unit 22 receives predetermined signalsthrough the antenna. The signals received by the RF unit 22 may bedesired packet signals as shown in FIG. 3 and interference signals otherthan the desired packet signals. The RF unit 22 is provided with anot-shown amplifier that amplifies the signal received by the RF unit22. Note that there are cases when the amplifier amplifies the packetsignal. The gain of the amplifier is set by the gain control unit 32described later. The RF unit 22 outputs the amplified baseband signal.

The power calculating unit 42 receives the input of the amplifiedbaseband signal from the RF unit 22. The power calculating unit 42averages the magnitudes of amplified baseband signals. Here, a movingaverage is taken over an average period. Two kinds of average period aredefined here. For convenience, a shorter period of two kinds thereof iscalled a “first average period” and a longer period a “second averageperiod”. Note also that the first average period is shorter than theperiod of STF. As a result, the power calculating unit 42 sequentiallyoutputs an average value obtained over the first average period and anaverage value obtained over the second average period.

The decision unit 44 sequentially receives from the power calculatingunit 42 the inputs of the average value over the first average periodand the average value over the second average period. The decision unit44 selects either the average value over the first average period or theaverage value over the second average period according to thenotification from the state management unit 38. The decision unit 44controls the gain of the amplifier based on the selected average value.The gain is determined such that the magnitude of the average value isbrought close to a target value. The processing performed by thedecision unit 44 will be later discussed in detail. The decision unit 44sequentially outputs the thus determined gain values to the instructionunit 46. The instruction unit 46 instructs the amplifier to use thegain, determined by the decision unit 44, at a predetermined frequency.That is, the instruction unit 46 has the amplifier use the controlledgain.

The STF correlation computing unit 34 receives the input of theamplified baseband signal from the RF unit 22. The STF correlationcomputing unit 34 computes cross-correlation between the amplifiedbaseband signal and the pattern of 16 samples in STF. The structure of acorrelator for computing the cross-correlation therebetween is known inthe art and therefore the repeated explanation thereof is omitted here.The STF correlation computing unit 34 sequentially outputs thecross-correlation to the rising-edge detector 36.

The rising-edge detector 36 receives the input of a correlation valuefrom the STF correlation computing unit 34. The rising-edge detector 36detects the receiving of STF in the packet signal. This corresponds todetecting the rising edge of the packet signal. More specifically, ifthe cross-correlation value becomes larger than a threshold value, therising-edge detector 36 will determine that a rising edge has beendetected and then convey the decision result to the state managementunit 38. To compute the rising edge thereof, the STF correlationcomputing unit 34 and the rising-edge detector 36 may monitor the signalstrength such as RSSI (Received Signal Strength Indication) instead ofcomputing the cross-correlation.

The state management unit 38 manages the receiving state of thereceiving apparatus 30. More specifically, the state management unit 38manages the state of whether the packet is being received or not. If anotification is received from the rising-edge detector 36 while nopacket signals is being received, the state management unit 38 willrecognize a transition to the state in which packet signals are beingreceived. For that purpose, the state management unit 38 is aware of theformat of the packet signal shown in FIG. 3 beforehand. Thus, in thestate where the packet signals are being received, the state managementunit 38 identifies if STF, LTF1, LTF2, SIG, or Data is being received.Thus, the state management unit 38 measures the timings after the startof the receiving of packet signal. To identify these, the statemanagement unit 38 may use the demodulation result and the decodingresult fed from the demodulation/receiving processing unit 40. The statemanagement unit 38 conveys, to the instruction unit 46, the state whereSTF is being received and the state where no packet signals is beingreceived.

The decision unit 44 receives, from the state management unit 38, thenotification regarding the state where STF is being received and thenotification regarding the state where no packet signals is beingreceived. Upon receiving the notification regarding the state where STFis being received, the decision unit 44 selects an average value takenover the first average period. Upon receipt of the notificationregarding the state where no packet signals is being received, thedecision unit 44 selects an average value taken over the second averageperiod. This corresponds to varying the length of average period by thepower calculating unit 42 according to the state of whether STF is beingreceived or no packet signals is being received. In particular, theformer average period is set longer than the later average period.

Upon receiving the notification regarding the state where STF is beingreceived, the decision unit 44 sets a predetermined target value(hereinafter referred to as a “first target value”). Upon receiving thenotification regarding the state where no packet signals is beingreceived, the decision unit 44 sets a target value, which is smallerthan the first target value, (hereinafter referred to as a “secondtarget value”). That is, decision unit 44 changes the magnitude of thetarget value according to the state of whether STF is being received orno packet signals is being received. In this manner, the powercalculating unit 42 performs different controls depending on the states.

FIG. 5 is a data structure of a table stored in the decision unit 44. Asshown in FIG. 5, the table is comprised of an STF period column 200 andan other-than-packet-signal column 202. A first average period (AP1) tobe used in the state where STF is being received and a first targetvalue (TV1) are shown in the STF period column 200. A second averageperiod (AP2) to be used in the state where no packet signals is beingreceived and a second target value (TV2) are shown in theother-than-packet-signal column 202. As described earlier, AP1<AP2 andTV1>TV2. The decision unit 44 selects the values indicated in the STFperiod column 200 or those indicated in the STF period column 200depending on the notification received from the state management unit38. Refer back to FIG. 4.

A further detailed description is now given hereunder of the processingperformed by the decision unit 44 in the state where STF is beingreceived. The decision unit 44 sets a target range in such a manner asto allow a marginal width around a given target value. The decision unit44 adjusts the gain until when an average value is contained in thetarget range. If, for example, the average value is lower than a lowerlimit, the decision unit 44 will increase the gain; if the average valueis higher than an upper limit, the decision unit 44 will reduce thegain. Such an adjustment will be made repeatedly during the period ofSTF.

FIGS. 6A and 6B show an operational overview of the decision unit 44.FIG. 6A indicates a comparative operation in the period of STF in thedecision unit 44. The horizontal axis corresponds to time. After apredetermined period has elapsed, a first comparison is made such thatan average value is compared against a target range. After apredetermined period has elapsed after the gain was controlled based onthe first comparison, a second comparison is made such that the averagevalue is again compared against the target value.

The reason why the process waits for a certain period of time asdescribed above is that time for response (response period) at theamplifier is taken into consideration. Such a process as described aboveis carried out repeatedly up to a fourth comparison in FIG. 6A. Notethat the number of comparisons is not limited to four times. FIG. 6Bwill be explained later. Refer back to FIG. 4.

If an average value is contained in the target value, the decision unit44 will fix the gain. The thus fixed gain is used over the remainingperiod of the packet signal. Thus, if, for example, the process is inthe middle of any of the first to third comparisons in the period ofSTF, the decision unit 44 will fix the gain and then omit the remainingcomparisons. If the average value is still not contained in the targetrange at the last comparison timing in the period of STF, namely by theend of the fourth comparison of FIG. 6A, the decision unit 44 will stopthe receiving of said packet signal. In other words, the packet signalwill be discarded because an appropriate gain has not been set. Toreduce such a probability of discarding the packet signal, the decisionunit 44 makes the width of target range, to be used at the last timingin the period of STF, wider than the previous width thereof.

FIG. 6B shows the first target values (TV1) and their target ranges setby the decision unit 44. A first range 210 is the target range used forthe comparisons except for the last comparison in the period of STF,namely for the first to third comparisons of FIG. 6A. As mentionedearlier, the first range 210 is so set as to allow a marginal widtharound TV1. A second range 212 is the target range used for the lastcomparison in the period of STF, namely for the fourth comparison ofFIG. 6A. The width of the second range 212 is so defined as to be widerthan that of the first range 210. Refer back to FIG. 4. The abovedescription corresponds to a case where the gain is less than themaximum value.

If, on the other hand, the gain is at the maximum value when comparisonis made, the decision unit 44 will perform the following processing. Ifthe gain is at the maximum value when the comparison is made, thedecision unit 44 will set a target range whose width is wider than thewidths of the target ranges at the time the gain is smaller than themaximum value (hereinafter, such a target value as this will be referredto as a “third range”). In FIG. 6B, the width of a third range 214 is sodefined as to be wider than both that of the first range 210 and that ofthe second range 212. Note that the width of the third range 214 needsonly to be wider than that of the first range 210 and therefore thewidth of the third range 214 may be narrower than or equal to that ofthe second range 212. In this manner, the decision unit 44 changes thewidth of a target range between when the gain is less than the maximumvalue and when the gain is at the maxim value. Refer back to FIG. 4.

The instruction unit 46 receives, from the state management unit 38, thenotification regarding the state where STF is being received and thenotification regarding the state where no packet signals is beingreceived. Immediately after it received the notification regarding thestate where STF is being received and immediately after it received thenotification regarding the state where no packet signals is beingreceived, the instruction unit 46 instructs the RF unit 22 to use aninitial value of the gain. The former corresponds to the timing withwhich the receiving of packet signal starts and the latter correspondsto the timing with which the receiving of packet signal ends.

FIG. 7 shows a structure of the instruction unit 46. The instructionunit 46 includes an initial value selector 50, a fixed value storage 52,and a most-recent value storage 54. The fixed value storage 52 storespredetermined gains (hereinafter referred to as “fixed values” or “fixedvalue”). The most-recent value storage 54 stores a most recent value ofthe gain that has been updated by the decision unit 44 in the statewhere no packet signals is being received (hereinafter referred to asthe “most recent value”). The most recent value is updated whenever thegain is updated. If the notification regarding the state where STF isbeing received is received while the notification regarding the statewhere no packet signals is being received is received, the initial valueselector 50 will extract a fixed value from the fixed value storage 52and instruct the RF unit 22 to use the fixed value. This corresponds tostarting to perform control by the gain control unit 32 using the fixedvalue as the initial value when the receiving of packet signal starts.

If, on the other hand, the notification regarding the state where nopacket signals is being received is received while the packet signal isbeing received, the initial value selector 50 will extract the mostrecent value from the most-recent value storage 54 and instruct the RFunit 22 to use the most recent value. This corresponds to starting toperform control by the gain control unit 32 using the most recent valueas the initial value when the receiving of packet signal starts. Themost recent value may be said to be the final value among the gains usedin the past for the signals other than the packet signals.

Such processings are now described hereunder based on FIG. 8. FIG. 8shows an operational overview of the instruction unit 46. The horizontalaxis indicates time. “T1” is the timing with which signals other thanthe packet signals are being received. At this time, the gain is “G1”that is the most recent value. Next, “T2” is the timing with which thereceiving of packet signal starts. At this time, the gain is “GC” thatcorresponds to the aforementioned fixed value. During a period of STF,the gain is controlled with the “GC” as the initial value, and then theremaining period is amplified with the resulting gain. “T3” is thetiming with which the receiving of packet signal ends. The gain at thistime is set to the then-most recent value “G1”.

In a period during which a signal other than the packet signal is beingreceived, the gain is controlled with the “G1” as the initial value;with the timing “T4”, the gain is updated to “G2”. The “G2” is now themost recent value. “T5” is the timing with which the receiving of packetsignal starts again. At this time, too, the gain is “GC”. “T6” is thetiming with which the receiving of packet signal ends again. At thistime, the gain is set to “G2” that is the then-most recent value. Thiscorresponds to the following. That is, when the receiving of a packetsignal, control is started using the final value of gain, which has beenused before the receiving of said packet signal, as the initial value.Refer back to FIG. 4.

As described earlier, the instruction unit 46 instructs the amplifier touse the gain, determined by the decision unit 44, at a predeterminedfrequency. A description is now given of the frequency at which the gainis used. The instruction unit 46 changes the frequency, at which thegain is updated, depending on a case when the instruction unit 46 isreceiving the notification regarding the state where STF is beingreceived or the notification regarding the state where no packet signalsis being received. More specifically, the instruction unit 46 lowers theupdate frequency when it is receiving the notification regarding thestate where no packet signals is being received than the updatefrequency when it is receiving the notification regarding the statewhere STF is being received.

FIG. 9 is a data structure of a table stored in the instruction unit 46.As shown in FIG. 9, the table is comprised of an STF period column 220and an other-than-packet-signal column 222. A first interval indicatedin the STF period column 220 is the interval at which the gain isupdated when the notification regarding the state where STF is beingreceived is received. A second interval indicated in theother-than-packet-signal column 222 is the interval at which the gain isupdated the notification regarding the state where no packet signals isbeing received is received. The first interval is shorter than thesecond interval. Here, the first interval is derived based on the firstaverage period and the response period required by the amplifier, andthe second interval is derived based on the second average period, theresponse period required by the amplifier and a waiting time period.

The second interval differs greatly from the first interval in thefollowing two points. The first point is that the second average periodis used instead of the first average period and the second point is thatthe waiting time period is appended in the second period. The waitingtime period is set to an arbitrary time length. Refer back to FIG. 4.The instruction unit 46 instructs the use of gain at each first intervalor second interval according to the content of notification. As the gainis fixed by the decision unit 44, the instruction unit 46 instructs theRF unit 22 to use the fixed gain until the packet signal ends. Thedemodulation/receiving processing unit 40 carries out the receivingprocessing in the modem unit 24 and the processing unit 26 of FIG. 2.

The present invention has been described based on the exemplaryembodiments. The exemplary embodiments are intended to be illustrativeonly, and it is understood by those skilled in the art that variousmodifications to constituting elements and processes as well asarbitrary combinations thereof could be further developed and that suchmodifications and combinations are also within the scope of the presentinvention.

An operation of the communication system 100 configured as above is nowdescribed. FIG. 10 is a flowchart showing a procedure, for setting anaverage period and a target value, performed by the receiving apparatus30. If a signal other the packet signals is received (Y of S10), thedecision unit 44 will set AP2 as the average period and set TV2 as thetarget value (S12). If, on the other hand, the signal other the packetsignals is not received (N of S10) but STF is received (Y of S14), thedecision unit 44 will set AP1 as the average period and set TV1 as thetarget value (S16). STF is not received (N of S14), the decision unit 44will not perform controlling (S18).

FIG. 11 is a flowchart showing a procedure, for controlling the gain,performed by the receiving apparatus 30. If the average value is withina target range (Y of S50), the decision unit 44 will fix the gain (S52).If, on the other hand, the average value is not within the target range(N of S50) and the comparison is the last comparison (Y of S56), thedecision unit 44 will stop the processing (S56). If the comparison isnot the last comparison (N of S56), the decision unit 44 will adjust thegain (S58).

FIG. 12 is a flowchart showing a procedure, for setting the ranges,performed by the receiving apparatus 30. If the gain is at the maximumvalue (Y of S60), the decision unit 44 will set the third rage (S62).If, on the other hand, the gain is not the maximum value (N of S60) andthe comparison is the last comparison (Y of S64), the decision unit 44will set the second range (S66). If the comparison is not the lastcomparison (N of S64), the decision unit 44 will set the first range(S68).

FIG. 13 is a flowchart showing a procedure, for storing the gain,performed by the receiving apparatus 30. If a signal other than thepacket signals is received (Y of S20) and the instruction unit 46outputs the gain (Y of S22), the gain will be stored in the most-recentvalue storage 54 (S24). If the signal other the packet signals is notreceived (N of S20) or the instruction unit 46 does not output the gain(N of S22), the processing will be completed.

FIG. 14 is a flowchart showing a procedure, for setting an initialvalue, performed by the receiving apparatus 30. If the timing is thestart timing of packet signal (Y of S30), the initial value selector 50selects a fixed value as the initial value (S32). If the timing is notthe start timing of packet signal (N of S30) and is the end timing ofpacket signal (Y of S34), the initial value selector 50 will set themost recent value as the initial value (S36). The instruction unit 46sets the initial value in the amplifier (S38). If the timing is not theend timing of packet signal (N of S34), the processing will becompleted.

FIG. 15 is a flowchart showing an instructing procedure performed by thereceiving apparatus 30. If a signal other than the packet signals isreceived (Y of S40), the instruction unit 46 will output the instructionat the second intervals (S42). If, on the other hand, the signal otherthe packet signals is not received (N of S40) and STF is received (Y ofS44), the instruction unit 46 will output the instruction at the firstintervals (S46). If STF is not received (N of S44), the processing willbe completed.

A description is now given of modifications of the exemplaryembodiments. A modification relates to the processing carried out by theinstruction unit. If the notification regarding the state where STF isbeing received is received while the notification regarding the statewhere no packet signals is being received is received, the instructionunit according to the exemplary embodiment starts to control the gaincontrol unit 32 using a fixed value as the initial value. If, on theother hand, the notification regarding the state where STF is beingreceived is received while the notification regarding the state where nopacket signals is being received is received, the instruction unitaccording to the modification will stat to control the gain control unit32 using the most recent value as the initial value. This processing issimilar to that performed in the case when the notification regardingthe state where no packet signals is being received is received whilethe packet signal is being received. The communication system 100according to the present modification is of a type similar to that ofFIG. 1, the radio apparatus 20 according to the present modification isof a type similar to that of FIG. 2, and the receiving apparatus 30according to the present modification is of a type similar to FIG. 4.Also, the instruction unit 46 according to the present modification isnot provided with the fixed value storage 52 of FIG. 7. A description isgiven here centering around different features.

If the notification regarding the state where STF is being received isreceived while the notification regarding the state where no packetsignals is being received is received, the initial value selector 50 ofFIG. 7 extracts the most recent value from the most-recent value storage54 and instructs the RF unit 22 to use the most recent value. Thiscorresponds to starting to perform control by the gain control unit 32using the most recent value as the initial value when the receiving ofpacket signal starts. If, on the other hand, the notification regardingthe state where no packet signals is being received is received whilethe packet signal is being received, the initial value selector 50 ofFIG. 7 extracts again the same most recent value from the most-recentvalue storage 54 and instructs the RF unit 22 to use the same mostrecent value. This corresponds to starting to perform another newcontrol by the gain control unit 32 using the most recent value as theinitial value when the receiving of packet signal starts.

Such processings are now described hereunder based on FIG. 16. FIG. 16shows an operational overview of an instruction unit 46 according to amodification of the exemplary embodiment. At “T1”, the gain is “G1” thatis the most recent value. Next, at “T2”, too, the gain is “G1” and themost recent value is used. During a period of STF, the gain iscontrolled with the “G1” as the initial value, and then the remainingperiod is amplified with the resulting gain. “T3” is the timing withwhich the receiving of packet signal ends. The gain at this time is setto the then-most recent value “G1”.

In a period during which a signal other than the packet signal is beingreceived, the gain is controlled with the “G1” as the initial value. Thegain is updated to the “G2” at “T4”. The “G2” is now the most recentvalue. At “T5”, too, the gain is “G2”. “T6” is the timing with which thereceiving of packet signal ends again. The gain at this time is set tothe then-most recent value “G2”.

A description is now given of another modification of the exemplaryembodiment. Similar to the above, the other modification of theexemplary embodiment relates also to the communication system thatcarries out both the inter-vehicular communication and theroad-to-vehicle communication and particularly relates to a receivingfunction implemented in a base station apparatus and terminalapparatuses in the communication system (hereinafter referred to as“receiving apparatus” as described above). In the exemplary embodiments,the receiving apparatus is equipped with a single antenna. On the otherhand, the receiving apparatus according to another modification isequipped with a plurality of antennas. The communication system 100according to another modification is of a type similar to that of FIG.1, and the radio apparatus 20 transmits packet signals from one of theplurality of antennas. A description is given here centering aroundfeatures different from the exemplary embodiments.

FIG. 17 shows a structure of a receiving apparatus 30 according toanother modification of the exemplary embodiment. The receivingapparatus 30 includes a first RF unit 22 a and a second RF unit 22 b,which are generically referred to as “RF unit 22” or “RF units 22”, again control unit 32, a first STF correlation unit 34 a and a second STFcorrelation unit 34 b, which are generically referred to as “STFcorrelation unit 34” or “STF correlation units 34”, a rising-edgedetector 36, a state management unit 38, and a demodulation/receivingprocessing unit 40. The gain control unit 32 includes a powercalculating unit 42, a decision unit 44, and an instruction unit 46.

The RF units 22 are so provided that each of the RF units 22 isassociated with each of the plurality of antennas on a one-to-onemanner. The number of antennas is two in this example but may be threeor more. The RF units 22 are so provided that the number of RF units 22corresponds to the number of antennas. The power calculating unit 42receives the inputs of the amplified baseband signals from therespective RF units 22. The power calculating unit 42 derives an averagevalue of each baseband signal over the first average period and anaverage value thereof over the second average period. Outputted here arenot only the average value of the baseband signal over the first averageperiod and the average value thereof over the second average period fedfrom the first RF unit 22 a but also the average value of the basebandsignal over the first average period and the average value thereof overthe second average period fed from the second RF unit 22 b.

Upon receiving the notification regarding the state where STF is beingreceived, the decision unit 44 selects a plurality of average valuestaken over the first average period. Upon receiving the notificationregarding the state where no packet signals is being received, thedecision unit 44 selects a plurality of average values taken over thesecond average period. In the former case, the average value of thebaseband signal over the first average period fed from the first RF unit22 a and the average value thereof over the first average period fedfrom the second RF unit 22 b are selected. In the latter case, theaverage value of the baseband signal over the second average period fedfrom the first RF unit 22 a and the average value thereof over thesecond average period fed from the second RF unit 22 b are selected.

If STF is being received, the decision unit 44 will select either one ofthem. For example, the larger one of the average value the basebandsignal over the first average period fed from the first RF unit 22 a andthe average value thereof over the first average period fed from thesecond RF unit 22 b is selected. The decision unit 44 performs theprocessing, similar to that of the exemplary embodiment, on the selectedaverage value. If no packet signals is being received, the decision unit44 will select either one of them. For example, the larger one of theaverage value the baseband signal over the second average period fedfrom the first RF unit 22 a and the average value thereof over thesecond average period fed from the second RF unit 22 b is selected. Thedecision unit 44 performs the processing, similar to that of theexemplary embodiment, on the selected average value. In these cases, thedecision unit 44 may select the smaller one them in the both cases. Orthe decision unit 44 may select the larger one of them in one of theabove cases and may select the smaller one of them in the other of theabove cases. Note that a statistical processing such as averaging may bedone instead of the selection made as above.

The STF correlation computing units 34 receive the inputs of theamplified baseband signals from the RF units 22, respectively. Each STFcorrelation computing unit 34 sequentially outputs correlation values tothe rising-edge detector 36. The rising-edge detector 36 receives theinputs of correlation values from the STF correlation computing unit 34,respectively. The rising-edge detector 36 detects the receiving of STFin the packet signal. In so doing, the rising-edge detector 36 mayselect any of the correlation values and then perform the processing,similar to that of the exemplary embodiment, on the selected averagevalue or may perform the processing, similar to that of the exemplaryembodiment, on a plurality of correlation values and then select any ofthe processed correlation values. Note that the rising-edge detector 36may select the large one of them and/or may select a correlation valuewhose detection timing is earlier. Further, the rising-edge detector 36may select the same one of them selected by the decision unit 44. Notealso that a statistical processing such as averaging may be done insteadof the selection made as above.

By employing the exemplary embodiments of the present invention,different controls are performed depending on a case when a known signalis received and a case when a signal other than the packet signal isreceived. Thus, the gain suited to the received packet signal can beset. Since the gain suited to the received packet signal is set, thereceiving quality can be improved. Also, the length of an average periodis changed depending on the case when a known signal is received or thecase when a signal other than the packet signal is received. Thus, thegains suited to the respective cases can be obtained. Since averagevalues suited to the respective cases are obtained, the accuracy in thesetting of gain can be improved. The average period when the signalother than the packet signals is received is set longer than that whenthe known signal is received, so that adverse effect of noise can bereduced. Since the adverse effect of noise is reduced, the processingcan be stabilized. The average period when the known signal is receivedis set shorter than that when the signal other than the packet signalsis received, so that the gain can follow and conform closely to thevariation in the received power. Since the gain follows and conformsclosely to the variation in the received power, the accuracy in thesetting of gain can be improved.

The length of the target value is changed depending on the case when theknown signal is received or the case when the signal other than thepacket signals are received, so that the gains suitable to therespective cases can be obtained. Since the gains suitable to therespective cases are obtained, the accuracy in the setting of gain canbe improved. Also, the magnitude of the target value in the case whenthe signal other than the packet signals is received is set smaller thanthat in the case when the known signal is received, so that theamplification of interference signal can be suppressed. Since theamplification of interference signal is suppressed, the probability thatpacket signal will be deformed can be reduced even though when thepacket signal is received. Since the probability of the packet signalwill be deformed is reduced, the receiving quality can be improved.Also, the magnitude of the target value in the case when the knownsignal is received is set larger than that in the case when the signalother than the packet signals is received. Thus, packet signals to bedemodulated can be sufficiently amplified. Since the packet signals tobe demodulated can be amplified sufficiently, the receiving quality canbe improved.

Also, the initial value is changed depending on the case when the knownsignal is received or the case when the signal other than the packetsignals is received, so that the gain suited to the received packetsignal can be set. Also, when the known signal is received, control isstarted using a predetermined gain as the initial value. Thus thedeviation in gain for the packet signal received with various powers canbe reduced. Since the deviation in gain is reduced, the receivingquality can be improved. When the signal other than the packet signalsis received, control is started using the gain, which is used in thepast for the signal other than the packet signals, as the initial value,thereby preventing the setting of the maximum gain. Since the setting ofthe maximum gain is prevented, the amplification of interference signalcan be suppressed. Also, when the receiving of packet signal has beencompleted, control is started using the final value of the gain, usedbefore said packet signal has been received, as the initial value. Thusa simplified processing can be executed.

Also, the gain suited to the received packet signal is set correspondingrespectively to the case when the known signal is received and the casewhen the signal other packet signals is received. Also, the updatefrequency in the case when the known signal is received is set higherthan that in the case when the signal other than the packet signals isreceived, so that the gain conforming closely to the variation in thereceived power can be set. Since the update frequency in the case whenthe signal other than the packet signals is received is set lower thanthat in the case when the known signal is received, the processingamount can be reduced. Since the amount of consumption is reduced, thepower consumption can be reduced. When the known signal is received, theuse of the gain is instructed for each interval based on the averageperiod and the response period at the amplifier, so that the gain can beinstructed quickly. When the signal other than the packet signals isreceived, the use of the gain is instructed based on the average periodand the response period at the amplifier, so that the update period canbe made longer. Also, the average period in the case when the signalother than the packet signals is received is set longer than that in thecase when the known signal is received, so that the update interval canbe made longer.

Also, the width of the target range in the case where the gain issmaller than the maximum value is made to differ from that in the casewhere the gain is the maximum value, so that the gain suited to thereceived packet signal can be set. Also, the width of the target rangewhere the gain is the maxim value is set wider than that where the gainis smaller than the maxim value. Thus, the average value is more likelyto be included in the target range when the gain is at the maximumvalue. Since the average value is more likely to be included in thetarget range when the gain is at the maximum value, the control of thegain can be stopped. Since the control of the gain is stopped, theprocessing amount can be reduced. Since the control of the gain isstopped, a large value can be kept as the gain. Since a large value canbe kept as the gain, the packet signal can be sufficiently amplified.When the gain is smaller than the maximum value, the width of the targetrange is made wider than the previous width of the target range beforethe end timing of the known signal. Thus the average value is morelikely to be included in the target range. Since the average value ismore likely to be included in the target range, the probability that thedemodulation of the packet signal will be stopped can be reduced.

In the respective cases where the known signal is received and where thesignal other than the packet signals is received, different controlsperformed while the same most recent value is used. Thus the gainssuitable to the respective cases can be set while the most recentpropagation environment is reflected and taken into consideration. Also,when the gain is to be controlled, a larger average value is selected.Thus, the gain can be determined based on the larger average value.Since the gain is determined based on the larger average value, theprobability that an overflow may occur in the analog-to-digitalconversion can be reduced. Since the probability of overflow is reduced,the receiving quality can be improved. Also, when the gain is to becontrolled, a smaller average is selected. Thus, the gain can bedetermined based on the smaller average value.

Since the gain is determined based on the smaller average value, theprobability that an underflow may occur in the analog-to-digitalconversion can be reduced. Since the probability of underflow isreduced, the receiving quality can be improved. Since a larger averagevalue or a smaller larger value is selected depending on a givencondition, the gain suited to the condition can be determined. Also, anyof a plurality of cross-correlation values is/are selected then thereceiving of STF in the packet is detected, so that an increase in theprocessing amount can be suppressed. Since STF is selected after aplurality of STFs in the packet signals have been received and detected,the detection accuracy can be improved.

The present invention has been described based on the exemplaryembodiments. The exemplary embodiments are intended to be illustrativeonly, and it is understood by those skilled in the art that variousmodifications to constituting elements and processes as well asarbitrary combinations thereof could be further developed and that suchmodifications and combinations are also within the scope of the presentinvention.

A general description of one embodiment of the present invention is asfollows. That is, a receiving apparatus according to one embodiment ofthe present invention includes: a receiving unit for receiving a signal;an amplifier for amplifying the signal received by the receiving unit;and a control unit for controlling a gain in the amplifier based on asignal amplified by the amplifier and having the amplifier use thecontrolled gain. The control unit performs different controls on thesignals received by the receiving unit, depending on a case when thereceived signal is a known signal placed in the beginning of packetsignal or a case when the received signal is a signal other than thepacket signal.

By employing this embodiment, the different controls are performeddepending on the case when the received signal is a packet signal havinga known signal placed in the beginning and the case when a signal otherthan the packet signal is received. Thus, the gain suited to thereceived packet signal can be set.

The control unit may include: an averaging unit for averaging themagnitude of signals amplified by the amplifier; and a decision unit fordetermining the gain such that the magnitude averaged by the averagingunit is brought close to a target value. The averaging unit may changean average period depending on a case when the signal received by thereceiving unit is a packet signal having a known signal placed in thebeginning or a case when the signal received by the receiving unit is asignal other than the packet signal. In this case, the average period ischanged depending on the case when the known signal is received or thecase when a signal other than the packet signal is received. In thisembodiment, the average period is changed depending on the case when theknown signal is received or the case when the signal other than thepacket signals is received, so that the average values suited to therespective cases can be obtained.

The averaging unit may set the average period of the signal received bythe receiving unit such that the average period of the signal other thanthe packet signal is longer than the average period of the known signalplaced in the beginning of the packet signal. In this embodiment, theaverage period when the signal other than the packet signals is receivedis set longer than that when the known signal is received, so thatadverse effect of noise can be reduced.

The control unit may include: an averaging unit for averaging themagnitude of signals amplified by the amplifier; and a decision unit fordetermining the gain such that the magnitude thereof averaged by theaveraging unit is brought close to a target value. The decision unit maychange the magnitude of the target value, depending on the case when thesignal received by the receiving unit is a known signal placed in thebeginning of packet signal or the case when the signal received by thereceiving unit is a signal other than the packet signal. In thisembodiment, the length of the target value is changed depending on thecase when the known signal is received or the case when the signal otherthan the packet signals are received, so that the gains suitable to therespective cases can be obtained.

The decision unit may set the target values of the signals received bythe receiving unit such that the magnitude of the target value of thesignal other than the packet signal is smaller than the magnitude of thetarget value of the known signal placed in the beginning of packetsignal. In this embodiment, the magnitude of the target value in thecase when the signal other than the packet signals is received is setsmaller than that in the case when the known signal is received, so thatthe amplification of interference signal can be suppressed.

Another embodiment of the present invention relates also to a receivingapparatus. The receiving apparatus includes: a receiving unit forreceiving a signal; an amplifier for amplifying the signal received bythe receiving unit; and a control unit for controlling a gain in theamplifier based on a signal amplified by the amplifier and having theamplifier use the controlled gain. When the signal received by thereceiving unit is a known signal placed in the beginning of packetsignal, the control unit starts to perform control using a predeterminedinitial value; when the receiving unit stops receiving the packetsignal, the control unit performs another control using thepredetermined initial value.

By employing this embodiment, the initial value is changed depending onthe case when the known signal is received or the case when the signalother than the packet signals is received, so that the gain suited tothe received packet signal can be set.

The control unit may use a final value of the gain used before thepacket signal has been received, as the initial value. In thisembodiment, when the signal other than the packet signals is received,control is started using the gain, which is used in the past for thesignal other than the packet signals, as the initial value, therebypreventing the setting of the maximum gain.

Still another embodiment of the present invention relates to a receivingapparatus. The receiving apparatus includes: a receiving unit forreceiving a signal; an amplifier for amplifying the signal received bythe receiving unit; and a control unit for controlling a gain in theamplifier based on a signal amplified by the amplifier and having theamplifier use the controlled gain. The control unit changes frequency,at which the gain is updated, depending on a case when the signalreceived by the receiving unit is a known signal placed in the beginningof packet signal or a case when the signal received by the receivingunit is a signal other than the packet signal.

By employing this embodiment, the update frequency is changed dependingon the case when the known signal is received or the case when thesignal other than the packet signals is received. Thus the gain suitableto the received packet signal can be set.

The control unit may set the frequency, at which the gain is updated,such that the frequency of update in the signal other than the packetsignal is lower than the frequency of update in the known signal placedin the beginning of packet signal. In this embodiment, the updatefrequency when the known signal is received is set higher than that whenthe signal other than the packet signals is received, so that the gainconforming closely to the variation in the received power can be set.

The control unit may include: an averaging unit for averaging themagnitude of signals amplified by the amplifier; a decision unit fordetermining the gain such that the magnitude thereof averaged by theaveraging unit is brought close to a target value; and an instructionunit for instructing the amplifier to use the gain determined by thedecision unit. When the signal received by the receiving unit is a knownsignal placed in the beginning of packet signal, the instruction unitmay instruct use of the gain for each interval, based on an averageperiod in the averaging unit and a response period at the amplifier;when the signal received by the receiving unit is the signal other thanthe packet signal, the instruction unit may instruct use of the gain foreach interval based on the average period in the averaging unit, theresponse period at the amplifier and waiting time period at theamplifier. In this embodiment, when the known signal is received, theuse of the gain is instructed for each interval based on the averageperiod and the response period at the amplifier, so that the gain can beinstructed quickly.

The averaging unit may set the average period of the signals received bythe receiving unit such that the average period of the signal other thanthe packet signal is longer than the average period of the packet signalhaving the known signal placed in the beginning. In this embodiment, theaverage period when the signal other than the packet signals is receivedis set longer than that when the known signal is received, so that theupdate interval can be made longer.

Still another embodiment of the present invention relates also to areceiving apparatus. The receiving apparatus includes: a receiving unitfor receiving a packet signal having a known signal placed in thebeginning; an amplifier for amplifying the packet signal received by thereceiving unit; and a control unit for controlling a gain in theamplifier based on the known signal in the packet signal amplified bythe amplifier and having the amplifier use the controlled gain. Thecontrol unit includes: an averaging unit for sequentially averaging themagnitude of a signal amplified by the amplifier in a period shorterthan that of the known period; and a decision unit for adjusting thegain until when the magnitude thereof averaged sequentially by theaveraging unit lies within a target range and for fixing the gain whenthe magnitude thereof averaged sequentially by the averaging unit lieswithin the target range. The decision unit sets the widths of the targetrange such that the width thereof in a case where the gain is smallerthan a maximum value differs from that in a case where the gain is themaximum value.

By employing this embodiment, the width of the target range in the casewhere the gain is smaller than the maximum value is made to differ fromthat in the case where the gain is the maximum value, so that the gainsuited to the received packet signal can be set.

The decision unit may set the widths of the target ranges such that thewidth thereof in the case where the gain is the maximum value is largerthan that in the case where the gain is smaller than the maximum value.In this embodiment, the width of the target range where the gain is themaxim value is set wider than that where the gain is smaller than themaxim value. Thus, the average value is more likely to be included inthe target range when the gain is at the maximum value.

When the gain is smaller than the maximum value, the decision unit mayenlarge the width of the target range from the previous target range.When the gain is smaller than the maximum value, the width of the targetrange is made wider than the previous width of the target range beforethe end timing of the known signal. Thus the average value is morelikely to be included in the target range.

What is claimed is:
 1. A receiving apparatus comprising: a receivingunit configured to receive a signal; an amplifier configured to amplifythe signal received by the receiving unit; a control unit configured tocontrol a gain in the amplifier based on the signal amplified by theamplifier and configured to have the amplifier use the controlled gain,the control unit including: an averaging unit configured to average amagnitude of the signal amplified by the amplifier; and a decision unitconfigured to determine the gain such that the magnitude of the signalaveraged by the averaging unit is brought close to a target value whenthe receiving unit receives the signal; and storage for storing a firstinitial value, which is a fixed value, to control the gain when thesignal received is a packet signal, and a second initial value, which isa variable value, to control the gain when the signal received is asignal other than the packet signal, the second initial value beingvaried and saved in the storage as a result of controlling the gain forthe signal other than the packet signal, wherein when the signalreceived by the receiving unit is the packet signal, the decision unitstarts to control the gain using the first initial value and changes thegain to a value different from the first initial value, when the signalreceived by the receiving unit following the packet signal is the signalother than the packet signal, the decision unit starts to control thegain using the second initial value and when the decision unit changesthe gain to a value different from the second initial value, the secondinitial value in the storage is updated by the value different from thesecond initial value, and wherein the decision unit changes a magnitudeof the target value, depending on the case when the signal received bythe receiving unit is a known signal placed in the beginning of packetthe signal or the case when the signal received by the receiving unit isthe signal other than the packet signal.
 2. The receiving apparatusaccording to claim 1, wherein the decision unit sets the target value ofthe signal received by the receiving unit such that the magnitude of thetarget value of the signal other than the packet signal is smaller thanthe magnitude of the target value of the known signal placed in thebeginning of the packet signal.